Carbon monoxide formation in fires by high-temperature anaerobic wood pyrolysis

Abstract

Building fire fatalities often occur at locations remote from the room where the fire is actually burning. The majority of these fire deaths are the result of smoke inhalation, primarily due to exposure to carbon monoxide (CO). Although causing nearly 2500 deaths per year in the United States, the mechanisms for the formation of CO in building or enclosure fires remain poorly characterized. In order to test the hypothesis that high concentrations of CO can be generated by pyrolysis of wood in a high-temperature, vitiated environment, a series of natural gas fires, ranging from 40 to 600 kW in heat release rate, were burned inside a reduced-scale enclosure (RSE). The ceiling and upper walls of the RSE were lined with 6.4-mm-thick plywood. During each burn, the concentrations of CO, CO 2 , and O 2 were monitored at two locations within the upper layer. Oxygen calorimetry was used to monitor the total heat release rate for each fire. Vertical temperature profiles for two positions within the enclosure were also recorded. Much higher levels of CO were generated with the wood-lined upper layer than with comparable fires fueled only by natural gas. Volume concentrations as high as 14% were observed. The fires with wood in the upper layer had higher heat release rates and depressed upper-layer temperatures. The major conclusions of this work based on the experimental findings are (1) the pyrolysis of wood in a highly vitiated, high-temperature environment can lead to the generation of very high concentrations of CO in enclosure fires; (2) the overall wood pyrolysis is endothermic for the experimental conditions studied; and (3) the maximum mass loss rate of wood under the experimental conditions is on the order of 10 gs −1 m −2 with the majority of released carbon being converted to a roughly 1:1 mixture of CO and CO 2 .